The continuation of currently active efforts to synthesize the two natural products aphidicolin and tirandamycin is proposed. Under the previous grant approaches were explored for each synthesis, and the outline of a particularly attractive and potentially efficient route to aphidicolin was developed. The rudiments of a viable tirandamycin synthesis also evolved from this work. It is proposed to render the aphidicolin synthesis to practice and prepare the natural product itself and several structural analogs. Modifications of the tirandamycin scheme are proposed so as to overcome stereochemical problems encountered in earlier work. The new synthetic scheme will lead to optically active material as the starting material will be sugar molecules. Both of these molecules are kn wn to act at the cellular level and inhibit DNA and/or RNA synthesis in bacteria and viruses. The mode of action of these drugs suggests that derivatives may be useful in cancer chemotherapy.